Heat pump unit

ABSTRACT

To prevent the decline in the volumetric efficiency and the decline in the performance of the heat pump having the reciprocating compressor integrated therein by decreasing the temperature of discharge gas in the reciprocating compressor with a simple construction, a heat pump unit  1  constituting a heat pump cycle in which the reciprocating compressor  3 , a condenser  5 , an expansion valve  7  and an evaporator  8  are interposed in a refrigerant circulating path  2 ,comprises a refrigerant-liquid returning path  9  for returning a portion of the refrigerant liquid having been condensed by the condenser  5  to a discharge chamber provided in a cylinder top assembly  20  of the reciprocating compressor  3  so that a portion of the refrigerant liquid is supplied to the discharge chamber  36  via the refrigerant-liquid returning path  9  and a discharge gas passageway  36 a is cooled by evaporative latent heat of the refrigerant liquid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior application Ser. No. 12/712,553, filed on Feb. 25, 2010, the disclosure of which, in its entirety, including the drawings, claims, and the specification, is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a heat pump unit and a reciprocating compressor which avoids temperature rise of refrigerant gas being discharged from the reciprocating compressor integrated in a heat pump unit such as a refrigeration unit so as to improve volumetric efficiency of the reciprocating compressor and further enhance capacity of the heat pump unit. The present invention also relates to a heat pump unit (including a refrigeration unit) using a reciprocating type compressor for NH₃ which is applicable to all kinds of reciprocating compressors regardless of whether it is a single-stage compressor or a two-stage compressor.

DESCRIPTION OF THE RELATED ART

A reciprocating type compressor that compresses gas by alternately opening and closing an intake valve and a discharge valve provided in a cylinder head or an upper part of a cylinder (hereinafter referred as a cylinder top assembly) by reciprocating the piston in the cylinder is well known in the art. Such reciprocating type compressor includes a single-stage reciprocating compressor in which gas drawn into the cylinder by the intake valve is compressed in a single stage and the compressed gas is discharged from the discharge valve, and a two-stage reciprocating compressor in which a compressing part thereof comprising the piston reciprocating in the cylinder includes a lower stage and an upper stage so that the gas compressed at the lower stage is further compressed at the upper stage. It is common that both the single-stage and the two-stage reciprocating compressors are provided with an intake gas passageway as well as a discharge gas passageway in a casing comprising a cylinder block. It is common in conventional cases to provide an intake gas passageway and a discharge gas passageway inside a casing thereof. In the reciprocating compressor integrated in the heat pump unit such as the refrigeration unit, heat exchange happens via a wall surface between discharge gas of high temperature and intake gas of low temperature and thus the temperature of the intake gas rises before being drawn into a cylinder. Therefore, the intake gas expands before reaching the cylinder and specific volume thereof becomes bigger and circulating mass flow decreases significantly. This brings decreased volumetric efficiency in the compressor and decline in cooling capacity of the refrigeration device in which the reciprocating compressor is integrated, or heating capacity of the heat pump unit.

Especially, ammonia gas has a relatively-high ratio of specific heat with such characteristics that the discharge temperature is high and the specific volume becomes larger as shown in FIG. 11. When using this type of refrigerant, it is necessary to suppress the heating (temperature rise) of the intake gas inside the casing of the compressor.

Patent Reference 1 P2000-18154A) discloses a means to suppress excessive temperature rise in the cylinder during the compression and to eliminate the problem of the deterioration of the lubricant and seizing. This means has cavities at the periphery of the cylinder and by introducing returning refrigerant (cooling medium) returning from an accumulator to the cavities so as to cool a cylinder room. The returning refrigerant passes the cavities and then leads to the intake chamber through communication holes.

[Patent Reference 1] JP2000-18154A

DISCLOSURE OF THE INVENTION Problems to be Solved

The means disclosed in Patent Reference 1 cools the cylinder by introducing the returning cooling media to the cavities provided at the periphery of the cylinder. Therefore, as the discharge gas is not cooled, there is heat exchange between the intake gas and the discharge gas via the wall surface of the casing and the temperature of the intake gas before reaching the cylinder inevitably rises. This brings decreased volumetric efficiency in the compressor and decline in cooling capacity of the refrigeration device in which the reciprocating compressor is integrated, or heating capacity of the heat pump unit.

Moreover, the cavities to which the refrigerant is introduced are provided around the cylinder room, resulting in a larger and heavier compressor, and a large amount of refrigerant is introduced to the cavities, resulting in decreasing the capacity of the heat pump device such as refrigeration device with the compressor.

In view of the problems above, embodiments of the present invention provide a heat pump unit (including a refrigeration unit) that prevents the temperature rise of the intake gas before being drawn into the cylinder, the heat pump unit being applicable to all kinds of reciprocating compressors for NH₃ regardless of whether it is a single-stage compressor or a two-stage compressor. In view of the problems above, embodiments of the present invention prevent the decline in the volumetric efficiency of the reciprocating compressor and the decline in the performance of the heat pump having the reciprocating compressor integrated therein by decreasing the temperature of the discharge gas in the reciprocating compressor with a simple construction.

Specifically, embodiments of the present invention provide a high-efficient heat pump device and refrigeration device using a reciprocating compressor in which cooling water is not used, the heating of the intake gas being suppressed, and the cooling capacity (volumetric efficiency) being improved.

Means to Solve the Problems

To solve the problem above, a heat pump of the present invention, is constructed so that the refrigerant liquid (condensed liquid) is injected to a refrigerant gas space of high temperature of the discharge side (discharge chamber or discharge area in communication with the discharge chamber) of the compressor so as to lower the temperature of the refrigerant gas being discharged, and comprises:

a heat pump cycle which includes a reciprocating compressor, a condenser, an expansion valve and an evaporator provided in a refrigerant circulating path: and

a first returning path for refrigerant liquid which returns a portion of the refrigerant liquid having been condensed in the condenser to a discharge chamber provided in a cylinder top assembly of the reciprocating compressor or a discharge area that is in communication with the discharge chamber,

wherein the portion of the refrigerant liquid is returned to the discharge chamber or discharge area via the first returning path so as to cool the discharge chamber or discharge area by evaporative latent heat of the refrigerant liquid.

The heat pump unit of the present invention is constructed to return a portion of the refrigerant liquid having been condensed in the condenser to the discharge chamber provided in the cylinder top assembly of the reciprocating compressor or the discharge area that is in communication with the discharge chamber. The refrigerant liquid is evaporated by the heat from the discharge gas in the discharge room or discharge area, and taking the evaporative latent heat from the discharge gas, thereby cooling the discharge chamber or discharge area. By cooling the discharge chamber or area, the heat transfer from the discharge chamber or area to the intake chamber or to the gas passageway is suppressed.

By this, the temperature rise of the refrigerant gas before being introduced to the cylinder is prevented, thereby suppressing the volume expansion and preventing the decline in the volumetric efficiency of the reciprocating compressor and the decline in the performance of the heat pump having the reciprocating compressor integrated therein.

In this manner, as the discharge chamber or discharge area being in communication with the discharge chamber is cooled by the evaporative latent heat of the refrigerant and there is no need for cooling water or the like, it is possible to use the heat pump in the desert or other places where the cooling water is hard to get. And this is very inexpensive and causes no damage to the environment.

The heat pump of the present invention preferably further comprises an injection nozzle which is arranged in the discharge chamber or discharge area and is connected to the first returning path for the refrigerant liquid,

wherein the refrigerant liquid is injected through the injection nozzle to the discharge chamber or discharge area. By this the evaporation of the refrigerant liquid at the discharge chamber or discharge area is promoted, thereby improving the cooling effect.

It is preferable in the heat pump unit of the present invention that the reciprocating compressor includes an upper stage compressor and a lower stage compressor, the first returning path for the refrigerant liquid returns the portion of the refrigerant liquid which have been discharged from the upper stage compressor and then condensed in the condenser, to the discharge chamber of the lower stage compressor or the discharge area that is in communication with the discharge chamber, and the portion of the refrigerant liquid is returned to the discharge chamber or discharge area of the lower stage compressor via the first returning path.

The refrigerant having been discharged from the upper stage compressor and then condensed in the condenser has higher pressure than the discharge chamber or discharge area of the lower stage compressor, and thus the refrigerant can be supplied to the discharge chamber or discharge area of the lower stage compressor without using an intensifier. Therefore, this pump unit does not require a power source or device for supplying the refrigerant liquid.

In addition to the configurations as described above, it is also preferable that the pump unit further comprises:

a second returning path for the refrigerant liquid which returns the portion of the refrigerant liquid having been discharged from the upper stage compressor and then condensed in the condenser, to the discharge chamber or discharge area; and

a pressure booster which is provided in the second returning path,

wherein the portion of the refrigerant liquid is returned to the discharge chamber or discharge area of the upper stage compressor via the second returning path.

When the portion of the refrigerant liquid is returned to the discharge chamber or discharge area of the upper stage compressor, a pressure booster such as a liquid pump needs to be provided in the returning path as the pressure booster and the discharge chamber or area of the upper stage compressor have the same pressure.

By this, the intake gas of the lower stage compressor and the upper stage compressor can be cooled.

The heat pump unit of the present invention preferably further comprises a heat exchanger for the refrigerant liquid which is provided in the refrigerant circulating path between the condenser and the expansion valve, the heat exchanger being connected to the refrigerant circulating path so that refrigerant gas discharged from the lower stage compressor is introduced to the intake chamber or intake area of the upper stage compressor through the heat exchanger, the refrigerant liquid from the condenser being cooled with the refrigerant gas discharged from the lower stage compressor.

By this, the refrigerant liquid moving in the circulating path from the condenser to the expansion valve is cooled by the refrigerant gas having been discharged from the upper stage compressor and having been cooled, thereby improving the performance of the heat pump such as refrigeration unit.

It is preferable that the heat pump unit of the present invention further comprises a heat exchanger for the refrigerant liquid which is provided in the refrigerant circulating path between the condenser and the expansion valve,

wherein the heat exchanger is connected to the refrigerant circulating path so that refrigerant gas discharged from the lower stage compressor is introduced to the intake chamber or intake area of the upper stage compressor, the refrigerant liquid from the condenser being cooled with the refrigerant gas discharged from the lower stage compressor,

wherein the heat exchanger for the refrigerant liquid is provided in the refrigerant circulating path in an upstream side of the first or second returning path, and

wherein a portion of the refrigerant liquid having been cooled in the heat exchanger is supplied to the first or second returning path.

By this, the refrigerant having been cooled by the heat exchanger can be supplied to the intake chamber or intake area of the lower stage or upper stage compressor, thereby making the upper stage compressor more effective in cooling the discharge gas.

It is preferable that the heat pump unit of the present invention further comprises an intercooler which is provided in the refrigerant circulating path between the condenser and the expansion valve, the intercooler being connected to the refrigerant circulating path so that refrigerant gas discharged from the lower stage compressor is supplied to the intake chamber or intake area of the upper stage compressor through the intercooler,

wherein a portion of the refrigerant liquid from the condenser is evaporated in the intercooler so as to cool other refrigerant liquid and the refrigerant gas discharged from the lower stage compressor.

By this, the performance of the heat pump unit is enhanced and the portion of the high-pressure refrigerant liquid having been over-cooled by the intercooler is supplied to the intake chamber or area of the lower stage compressor so as to improve the cooling effect of the discharge gas of the lower stage compressor and reduce the supply of the refrigerant liquid. Thus, the injection nozzle provided in the discharge chamber or area of the lower stage compressor can be downsized.

In the case of using NH₃ which has high ratio of specific heat as refrigerant, there is such characteristic that when the temperature rises, the specific volume of NH₃ gets bigger than other types of refrigerant. The volume expansion of the refrigerant due to the temperature rise of the intake gas before reaching the cylinder is significant. However, with the present invention, the temperature rise of NH₃ before being introduced to the cylinder is securely suppressed, thereby avoiding the declined performance of the heat pump unit.

Next, a first reciprocating compressor of the present invention that can be applied to the heat pump unit of the present invention is a reciprocating compressor for refrigerant which is equipped with an intake chamber connected to a cylinder via an intake valve at a cylinder top assembly and a discharge chamber connected to the cylinder via a discharge valve, the reciprocating compressor comprising:

a supply port for refrigerant liquid which is provided in the discharge chamber or a discharge area that is in communication with the discharge chamber and through which a portion of the refrigerant liquid obtained by condensing discharge gas is supplied to the discharge chamber or discharge area,

wherein the supplied refrigerant liquid evaporates in the discharge chamber or discharge area so that the discharge chamber or discharge area is cooled by evaporative latent heat of the refrigerant liquid.

With the configuration described above, the portion of the refrigerant liquid obtained from condensing the discharge gas is supplied to the discharge chamber or area, thereby cooling the discharge chamber or area by the evaporative latent heat of the refrigerant liquid. Consequently the temperature rise in the discharge chamber or area is diminished and the temperature rise of the intake gas before being introduced to the cylinder is prevented. Thus, the increase of the specific volume of the intake gas is suppressed and the declined volumetric efficiency is avoided.

In the first reciprocating compressor of the present invention, the compressor further comprises an injection nozzle which is arranged in the discharge chamber or discharge area and is connected to the supply port for the refrigerant liquid,

wherein the refrigerant liquid is injected through the injection nozzle to the discharge chamber or discharge area.

By this, the evaporation of the refrigerant liquid in the discharge chamber or area is enhanced, thereby improving the cooling effect of the refrigerant liquid.

Moreover, a second reciprocating compressor of the present invention that can be applied to the heat pump unit of the present invention for refrigerant which is equipped with an intake chamber connected to a cylinder via an intake valve at a cylinder top assembly and a discharge chamber connected to the cylinder via a discharge valve, is unique in that a heat insulating material is interposed between the intake chamber and the discharge chamber so as to suppress heat transfer between the intake chamber and discharge chamber.

With the configuration described above, by simply interposing a heat insulating material between the intake chamber and the discharge chamber, the heat transfer between the intake chamber and discharge chamber is prevented. Consequently, the temperature rise of the refrigerant gas before reaching the cylinder is prevented, thereby suppressing the increase of the specific volume of the refrigerant gas and suppressing the decline in the volumetric efficiency. Thus, the performance of the heat pump unit integrating the reciprocating compressor is maintained.

Furthermore, by combining the first reciprocating compressor and the second reciprocating compressor, it is possible to suppress the heat transfer from the discharge chamber to the intake chamber in a synergistic manner.

Specifically, the supply port is provided in the discharge chamber or area for receiving the portion of the refrigerant gas obtained by condensing the discharge gas is provided; the refrigerant liquid is supplied to the discharge chamber or area via the supply port; the discharge chamber or area is cooled by the evaporative latent heat of the refrigerant liquid; and the insulating material is interposed between the discharge chamber and intake chamber so as to effectively suppress the heat transfer from the discharge chamber to the intake chamber.

In the first or second reciprocating compressor of the present invention, it is preferable that

the cylinder top assembly comprises: a closure plate which closes the cylinder so as to form a discharge gas passage and having the discharge valve at the discharge gas passage; a head cover which covers over the closure plate so as to form the discharge chamber; a valve plate which is arranged under the closure plate so as to enclose the cylinder and in which the intake valve is provided; a cylinder exterior body which is arranged under the valve plate and forms the intake chamber, and

wherein an insulation gasket is interposed between the valve plate and the cylinder exterior body,

wherein the valve plate and gasket are widen at edges thereof so as to grip and hold outer edges of the valve plate and the insulation gasket at a joint part of the head cover and the cylinder exterior body from both sides.

With the configuration described above, the insulation gasket can be easily fixed between the valve plate and the cylinder exterior body. And by interposing the insulation gasket between the valve plate and the cylinder exterior body, the blocking between the intake chamber formed by the cylinder exterior body and the discharge chamber formed above the closure plate is effectively done.

Furthermore, when the cylinder exterior body encloses a plurality of the cylinders, it is preferable to form an insulation space between the cylinder exterior body and the gasket in an area interposed by the cylinders. By this, the insulation effect can be further enhanced.

Effect of the Present Invention

With the heat pump unit of the present invention comprising a heat pump cycle which includes a reciprocating compressor, a condenser, an expansion valve and an evaporator provided in a refrigerant circulating path: and a first returning path for refrigerant liquid which returns a portion of the refrigerant liquid having been condensed in the condenser to a discharge chamber provided in a cylinder top assembly of the reciprocating compressor or a discharge area that is in communication with the discharge chamber, wherein the portion of the refrigerant liquid is returned to the discharge chamber or discharge area via the first returning path so as to cool the discharge chamber or discharge area by evaporative latent heat of the refrigerant liquid, the heat transfer from the discharge chamber or area to the intake chamber or area of the reciprocating compressor is suppressed and the temperature rise and volume expansion of the intake gas before being introduced to the cylinder is suppressed, and the volumetric effect of the reciprocating compressor is prevented from declining. By this, even when the refrigerant with high specific volume such as NH₃ is used, the performance of the heat pump unit is maintained. Furthermore, by not using the cooling water, it is possible to use the heat pump in the desert or other places where the cooling water is hard to get. And this is very inexpensive and causes no damage to the environment.

With the first reciprocating compressor of the present invention for refrigerant which is equipped with an intake chamber connected to a cylinder via an intake valve at a cylinder top assembly and a discharge chamber connected to the cylinder via a discharge valve, the reciprocating compressor comprising: a supply port for refrigerant liquid which is provided in the discharge chamber or a discharge area that is in communication with the discharge chamber and through which a portion of the refrigerant liquid obtained by condensing discharge gas is supplied to the discharge chamber or discharge area, wherein the supplied refrigerant liquid evaporates in the discharge chamber or discharge area so that the discharge chamber or discharge area is cooled by evaporative latent heat of the refrigerant liquid, the heat transfer from the discharge chamber or area to the intake chamber or area of the reciprocating compressor is suppressed and the temperature rise and volume expansion of the intake gas before being introduced to the cylinder is suppressed, and the volumetric effect of the reciprocating compressor is prevented from declining. And by applying this to the aforementioned heat pump unit of the present invention, it is possible to maintain the performance of the heat pump unit.

With the second reciprocating compressor of the present invention that can be applied to the heat pump unit of the present invention for refrigerant which is equipped with an intake chamber connected to a cylinder via an intake valve at a cylinder top assembly and a discharge chamber connected to the cylinder via a discharge valve, wherein a heat insulating material is interposed between the intake chamber and the discharge chamber so as to suppress heat transfer between the intake chamber and discharge chamber, the heat transfer from the discharge chamber or area to the intake chamber or area of the reciprocating compressor is suppressed with a simple means and the effects similar to that of the first reciprocating compressor of the present invention is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a refrigeration unit relating to first embodiment of the present invention.

FIG. 2 is an elevation plan of a cylinder top assembly of the reciprocating compressor to be integrated in the refrigeration unit of the first embodiment.

FIG. 3 is a perspective interior elevation of the cylinder top assembly of the reciprocating compressor of the first embodiment.

FIG. 4 is a system diagram of a refrigeration unit relating to second embodiment of the present invention.

FIG. 5 is a system diagram of a refrigeration unit relating to third embodiment of the present invention.

FIG. 6 is a system diagram of a refrigeration unit relating to fourth embodiment of the present invention.

FIG. 7 is a system diagram of a refrigeration unit relating to fifth embodiment of the present invention.

FIG. 8 is a system diagram of a refrigeration unit relating to sixth embodiment of the present invention.

FIG. 9 is an elevation plan of a cylinder top assembly of the reciprocating compressor to be integrated in the refrigeration unit of a seventh embodiment.

FIG. 10 is a system diagram of a refrigeration unit relating to an eighth embodiment of the present invention.

FIG. 11 is a graph showing the change of specific volume of ammonia gas.

FIG. 12 is a system diagram of a refrigeration unit relating to ninth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component described in these embodiments shall not be construed as limiting the scope of the invention thereto, unless especially specific mention is made.

First Embodiment

A first embodiment of the present invention which is applied to the refrigeration unit is explained in reference to FIG. 1 to FIG. 3. FIG. 1 is a system diagram of a refrigeration unit relating to first embodiment of the present invention (a reciprocating compressor 3 being a single-stage compressor).

In FIG. 1 a refrigeration unit 1 is equipped with a refrigerant circulating passageway for refrigerant MH³, and on the passageway the reciprocating compressor 3, from there down, an oil separator 4, a condenser 5, a liquid receiver 6, an expansion valve 7, an evaporator 8 are interposed so as to configure a cooling cycle.

The reciprocating compressor 3 has a discharge chamber 303 being connected to the cylinder 301 via a discharge valve 302 and an intake chamber 305 being connected to the cylinder via a intake valve 304. The discharge chamber 303 is provided at an immediate exit side of the discharge valve 302 and being connected to the refrigerant circulating passageway 2. The intake chamber 305 is provided at an immediate exit side of the intake valve and being connected to the refrigerant circulating passageway 2. The refrigerant gas having been compressed to high pressure in the cylinder is discharged via the discharge valve 302 to the discharge chamber 303.

The refrigerant gas having been discharged from the discharge chamber to the refrigerant circulating passageway 2 is passed through the oil separator 4 so as to separate lubricant oil, and then is sent to the condenser 5 so as to promote heat loss and condense the refrigerant gas. The condensed refrigerant gas is temporarily stored in the evaporator 8 where evaporative latent heat is absorbed from a load. Subsequently, the refrigerant gas is introduced to the intake chamber 305 of the reciprocating compressor 3 and then to the cylinder 301 via the intake valve 304. The temperatures shown at each part on the circulating passageway in FIG. 1 are the temperatures of the refrigerant (NH3) at those parts.

In the embodiment, a branching path 9 for diverging the refrigerant liquid from the refrigerant circulating passageway in the downstream of the liquid receiver 6 is provided. The branching path 9 is connected to an injection nozzle 306 located on an inner wall of the discharge chamber 303. A liquid pump 11 and a pressure-regulating valve 12 located in the downstream side of the liquid pump are interposed in the branching path 9. A portion of the refrigerant liquid passes through the branching path 9 so as to adjust the pressure thereof by the rotation speed control of the liquid pump 11, and the pressure-regulating valve 12, becoming high-pressure in the discharge chamber 303, and being sprayed from the injection nozzle 306 into the discharge chamber 303. The refrigerant liquid having been injected into the discharge chamber 303 evaporates while absorbing evaporative latent heat if the refrigerant gas in the discharge chamber 303.

In this manner, the heat transfer from the discharge chamber to the intake chamber is suppressed so as to lower the temperature inside the discharge chamber. Thus, the temperature rise of the refrigerant gas before being introduced into the cylinder 301 is suppressed.

In the embodiment, an air condensing apparatus is used for the condenser 5 and a high pressure type or expansion type oil cooler (not shown in the drawings) is used for cooling the lubricant oil of the reciprocating compressor 3 so that a high efficient heat pump unit or refrigeration unit having the reciprocating compressor which does not use cooling water is achieved.

Moreover, it is also possible to arrange the liquid receiver 6 in an upstream side of the reciprocating compressor 3 in the direction of gravitational force and provide a liquid head so as to omit the liquid pump 11 (this can be applied to other embodiments described below)

FIG. 2 and FIG. 3 illustrate detailed constructions of a cylinder top assembly of the reciprocating compressor 3. The reciprocating compressor 3 of the present embodiment has two cylinders.

In FIG. 2, a piston 22 is slidably positioned in the cylinder 21. The cylinder 21 is placed on an exterior body 23. On top of the cylinder exterior body 23, a valve plate 31 is positioned which has openings 31 a. The openings 31 a are positioned to correspond to the top opening of the cylinders 21. The valve plate 31 has cavities in which the plate-type intake valve 25 forming a ring shape and a volute spring 26 on top of the intake valve are housed.

An elastic force of the volute spring 26 works on the intake valve 25 so as to press the intake valve 25 against a valve seat 27 located on top of the cylinder 21. The intake chamber is located under the intake valve and the intake chamber is in communication with the cylinder 21 by lifting the intake valve 25 with the refrigerant gas against the elastic force of the volute spring working on the intake valve 25.

A valve cage 32 in a shape of circular plate is provided above the valve plate 31 so as to close the opening 31 a of the valve plate 31. A valve plate 34 in a shape of a conical frustum is joined to the bottom of the valve cage 32 with a bolt 33. A positioning pin 35 is inserted in a positioning hole of the valve plate 34 and a positioning hole of the valve cage 32 so as to position the valve plate 34 in respect with the valve cage 32. The valve plate 34 is shaped to fit in the top part of the piston 22 and when the piston 22 reaches the top limit of the cylinder 21, there is no space in the cylinder.

A discharge gas passage 36 a is formed in the valve cage 32 and the volute spring 37 is provided in the discharge gas passageway 36 a. Under the volute spring, a discharge valve 38 in a shape of a ring plate is provided. Under the discharge valve 38, a the valve seat 34 a and another valve seat 31 b integral with the valve plate 31 are arranged. When the pressure of the discharge gas of the cylinder 21 is small, the elastic force of the volute spring 37 works on the discharge valve 38 so as to press the discharge valve 38 against the valve seats 34 a and 31 b, thereby closing the discharge gas passageway 36 a. When the piston 22 is lifted and the pressure of the discharge gas becomes larger, the discharge gas lifts the discharge valve 38 so as to open the discharge gas passageway 36 a.

A plate-like insulation gasket 39 made of insulation material is interposed between the valve plate 31 and the cylinder exterior body 23. Above the valve cage 32, a head cover 40 is arranged so as to form a discharge chamber 36 on top of the valve cage 32. The discharge chamber 36 is in communication with the discharge gas passageway 36 a and also feeds the high-pressure discharge gas being discharged from the cylinder 21 to the refrigerant circulating path 2. The branching path 9 is connected to a through-bore 40 a formed in the head cover, and an injection nozzle 306 is provided in the opening of an inner wall of the head cover. By this, the refrigerant liquid of the branching path 9 is sprayed into the discharge chamber 36.

As shown in FIG. 3, a bolt seat 41 is arranged at the outer edge of the head cover 40, and bolt holes 42, 43, 44 and 45 are provided at the outer edge of the bolt seat 41, valve plate 31, insulation gasket 39 and cylinder exterior body 23 respectively which are integrally connected with bots not shown in the drawings.

Moreover, in the present embodiment, the exterior body 23 of the cylinder is constructed to include two cylinders. Thus, the exterior body 23 has two openings 23 a in which two cylinders are fitted. And between the pair of the openings 23 a, a depressed portion 46 is provided so as to form an insulation space i between the exterior body 23 and the insulation gasket 39.

In the reciprocating compressor of FIG. 2 and FIG. 3, the piston 22 moves downward and thus forming low pressure in the cylinder 21 and the intake gas g₁ pushes up the intake valve 25 against the elastic force of the spring 26 so as to introduce the intake gas g₁ into the cylinder 21. Next the piston 22 moved upward and it becomes high pressure inside the cylinder, and the discharge gas g₂ pushes up the discharge valve 38 against the elastic force of the volute spring 37 so as to discharge the discharge gas g₂ of high pressure to the discharge chamber 36 via the discharge gas passageway 36 a.

When the reciprocating unit is housed in the refrigeration unit 1, for instance, the temperature of the intake chamber 24 is −20 to 0° C., the intake pressure being 0.2 to 0.4 Mpa, the temperature of the discharge chamber 36 being 120 to 140° C. and the discharge pressure being 1.3 to 1.6 Mpa.

The cylinder top assembly 20 is heated by the heated discharge gas g₂. However, in the present embodiment, the refrigerant liquid is sprayed from the branching path 9 into the discharge chamber 36 via the injection nozzle 306, the sprayed refrigerant liquid cooling the discharge gas by the evaporative latent eat of the discharge gas, and the insulation gasket 39 being interposed between the valve plate and the cylinder exterior body 23 so as to suppress effectively the heat transfer from the discharge gas g₂ through the exterior body 23 to the intake gas g₁ moving through the intake chamber.

In this manner, the temperature rise of the intake gas g₁ before being introduced to the cylinder 21 is suppressed, thereby inhibiting the volumetric expansion of the intake gas g₁. For instance, as shown in FIG. 1, the refrigerant liquid of 35° C. is injected to the injection nozzle 306 so as to reduce the temperature of the discharge gas inside the discharge chamber 303 to 50° C. and reduce the temperature of the intake gas inside the intake chamber 305 to −10° C. Thus, the volume expansion of the refrigerant gas being introduced to the cylinder is prevented, thereby suppressing the decline of the volumetric efficiency of the reciprocating compressor 3. In this manner, the performance of the reciprocating compressor integrated in the refrigeration unit 1 is maintained.

Especially, NH₃ which is used as refrigerant has high ratio of specific heat and the volume expansion due to the temperature rise is significant and thus the decline of the volumetric efficiency of the reciprocating unit becomes large. However, with the present invention, the decline of the volumetric efficiency of the reciprocating unit is suppressed and the performance of the refrigeration unit 1 is sustained.

Moreover, in the present embodiment, the temperature of the intake gas is suppressed by the evaporative latent heat of the refrigerant liquid and the insulation gasket 19 and does not require cooling water. Therefore, it is possible to use the heat pump in the desert or other places where the cooling water is hard to get. And this is very inexpensive and causes no damage to the environment.

In the present embodiment, the refrigerant liquid is sprayed to the discharge chamber 36 in a form of fine particles through the injection nozzle 306 so as to improve the absorption effect of the evaporative latent heat of the discharge gas. Moreover, the insulation gasket 39 is installed from the intake chamber 24 to the outer edge of the cylinder exterior body 23 so as to shut off the heat of the discharge gas in a wide range where the insulation gasket 39 is installed. Therefore, the heat transfer of the discharge gas to the cylinder exterior body 23 is effectively prevented.

Additionally, the insulation space i is provided in the cylinder exterior body 23 and between the plural cylinders 21 so as to improve the heat insulation effect.

Second Embodiment

Next, a second embodiment of the present invention (the reciprocating compressors 3 a, 3 b are combined two stage compressor or individual two stage compressors without an intercooler in the refrigerant path 2 a between a liquid receiver 6 and an expander 7 in the two-stage compression and the single-stage expansion) is explained in reference to FIG. 4. In FIG. 4, a refrigeration unit 1 has a two-stage reciprocating compressor consisting of a lower stage compressor 3 a and an upper stage compressor 3 b. The configuration of the cylinder top assembly of the lower and upper stage compressors 3 a and 3 b are the same as that of the compressor of the first embodiment shown in FIG. 2 and FIG. 3.

The refrigerant liquid from the liquid receiver 6 passes through the refrigerant circulating path 2 a and reaches the expansion valve 7. The refrigerant liquid is decompressed by the expansion valve 7, the decompressed refrigerant liquid evaporating in the evaporation unit 8 by taking the evaporative latent heat from, and the evaporated refrigerant gas being introduced to the intake chamber 305 of the lower stage compressor 3 a. The refrigerant gas being introduced to the intake chamber 305 is then introduced to the cylinder 301 via the intake chamber 304 and compressed in the cylinder 301.

The refrigerant gas being compressed in the cylinder 301 is fed to the discharge chamber 303 via the discharge valve 302, and then discharged from the discharge chamber 303 to the refrigerant circulating path 2 b. The refrigerant gas being discharged form the refrigerant circulating path 2 b is filtered in the oil separator 4 a so as to separate the lubricant oil and then introduced into the intake chamber 305 of the upper stage compressor 3 b.

The refrigerant gas being introduced to the intake chamber 305 of the upper stage compressor 3 b is compressed in the cylinder 301 of the upper stage compressor 3 b and then discharged form the discharge chamber 303 to the circulating path 2 c. The refrigerant gas being discharged to the circulating path 2 c is filtered by the oil separator 4 b so as to separate the lubricant oil and the filtered refrigerant gas releases the heat and condensed in the condenser 5.

In the present embodiment, a branching path 51 is provided which branches from the refrigerant circulating path 2 a in the downstream side of the liquid receiver 6. In the branching path 51, a liquid pump 52 and a pressure regulating valve 53 are provided. The terminal of the branching path 51 is connected to the discharge chamber of the upper stage compressor 3 b. By the rotation speed control of the liquid pump 52, and the pressure control of pressure-regulating valve 53, the refrigerant liquid is pressurized to a higher pressure than that of the discharge chamber 303 of the upper stage compressor 3 b and sprayed into the discharge chamber 303 via the injection nozzle 306.

Another branching path 54 branches from the circulating path 2 a in the downstream side of the branching path 51 and the branching path 54 is connected to the injection nozzle 306 provided on the inner wall of the discharge chamber 303 of the lower stage compressor 3 a. Inside of the discharge chamber 303 of the lower stage compressor 3 a has a lower pressure than the branching path 54, and thus there is no need for increasing the pressure of the refrigerant liquid and the refrigerant liquid can be supplied to the discharge chamber 303 without increasing the pressure.

In the present embodiment, the refrigerant liquid is sprayed into the discharge chamber 303 of the upper stage compressor 3 b and the lower stage compressor 3 a from the branching path 51 and 54, and the sprayed refrigerant liquid is evaporated in the discharge chamber 303 with the potential heat of the discharge gas, and the evaporative latent heat is taken from the discharge gas so as to cool the discharge gas. Therefore, the heat transfer from the discharge chamber 303 to the intake chamber 305 in the lower stage compressor 3 a and the upper stage compressor 3 b is prevented.

As shown in FIG. 2 and FIG. 3, in the cylinder head 20 of the lower stage compressor 3 a and the upper stage compressor 3 b, the insulation gasket 39 is interposed between the valve plate 31 and the cylinder exterior body 23 so as to suppress the heat transfer from the discharge chamber to the intake chamber by the insulation gasket 39.

As shown in FIG. 4, the temperature of the intake chamber 305 of the lower stage compressor 3 a is suppressed to −25° C. and the temperature of the intake chamber 305 of the upper stage compressor 3 b is suppressed to 15° C. so as to prevent the decline of the volumetric efficiency of the reciprocating compressor and further maintain the performance of the refrigeration unit 1.

The pressure in the discharge chamber 303 of the upper stage compressor 3 b and that of the branching path 51 are the same and thus when supplying the refrigerant liquid to the discharge chamber 303 of the upper stage compressor 3 b from the branching path 51, it does not require the pressure regulating valve 53 to increase the pressure of the refrigerant liquid by the liquid pump 52 and the pressure regulating valve 53. On the other hand, the discharge chamber 303 of the lower stage compressor 3 a has low pressure and thus when supplying the refrigerant liquid from the branching path 54 to the discharge chamber 303 of the lower stage compressor 3 a, it does not need pressure intensifying. Therefore, the pressure booster is not needed and it requires less power.

The temperature of the intake gas of the lower stage compressor 3 a is lower than that of the intake gas of the upper stage compressor. For instance, the temperature of the intake gas of the lower stage compressor 3 a is −30° C. and the temperature difference of the lower stage compressor is large compared to that of the upper stage compressor. Therefore, the temperature rise of the intake gas due to the heat transfer from the discharge gas affects the lower stage compressor 3 a more than the upper stage compressor 3 b. And by supply the refrigerant liquid to the discharge chamber 303 of the lower stage compressor 3 a to the branching path 54, the temperature suppressing effect of the intake gas is enhanced and the decline of the cooling capability is avoided.

Third Embodiment

Next, a third embodiment of the present invention (Case 1 of a single stage expansion and the two stage reciprocating compressors 3 a, 3 b with an intercooler. The intercooler 61 feeds the refrigerant liquid in the side of the liquid receiver 6 to the expansion valve 7 and the evaporation unit 8 via a heat-transfer pipe 61 and the refrigerant liquid is not decompressed in the intercooler 61) is explained in reference to FIG. 5. In FIG. 5, a heat exchanger 61 for liquid gas is provided in the refrigerant circulating path 2 a in the downstream side of the liquid receiver 6, and to the heat exchanger, connected is the refrigerant circulating path 2 b of the downstream side of the oil separator 4 a. And heat exchange take place in the heat exchanger 61 between the refrigerant liquid from the liquid receiver 6 and the discharged refrigerant gas in the downstream side of the oil separator 4 a, and the refrigerant liquid is cooled by the discharge refrigerant gas.

The refrigerant liquid from the liquid receiver 6 passes through the refrigerant circulating path 2 a and reaches the expansion valve 7. The refrigerant liquid is decompressed by the expansion valve 7, the decompressed refrigerant liquid evaporating in the evaporation unit 8 by taking the evaporative latent heat from, and the evaporated refrigerant gas being introduced to the intake chamber 305 of the lower stage compressor 3 a. The refrigerant gas being introduced to the intake chamber 305 is then introduced to the cylinder 301 via the intake chamber 304 and compressed in the cylinder 301. The rest of the configuration is the same as that of the second embodiment shown in FIG. 4 and the same devices or units have the same reference numbers as the second embodiment, which will not be further explained herein.

The refrigerant liquid of the downstream side of the liquid receiver is supplied to the discharge chamber 303 of the lower stage compressor 3 a via the branching path 54, and as shown in FIG. 2, is sprayed into the discharge chamber 303 via the injection nozzle 306. Next, the refrigerant liquid is evaporated so as to lower the temperature of the discharge gas inside the discharge chamber 303. For instance, if the condensation temperature is 35° C. and the evaporation temperature is −30° C., the temperature of the refrigerant liquid in the condenser 5 and the liquid receiver 6 is 35° C. and the refrigerant liquid is evaporated in the discharge chamber 303 and the evaporative latent heat is absorbed so as to lower the temperature of the discharge gas in the discharge chamber 303 to 10° C.

The discharge gas having been cooled to 10° C. is introduced to the heat exchanger 61 in which the refrigerant liquid having the temperature 35° C. from the liquid receiver 6 is cooled to 30° C. in the heat exchanger 61.

In this manner, with the present embodiment, the similar function effect to the second embodiment is obtained and by cooling the refrigerant liquid at the exit side of the liquid receiver 6 by the discharge gas of the lower stage compressor 3 a in the heat exchanger 61, the refrigeration capability of the refrigeration unit 1 is further enhanced and COP can be improved.

In the upper stage compressor 3 b, the head cover (discharge chamber 303) may be cooled by water instead of injection of the refrigerant liquid (injection nozzle 306), or maybe cooled by air depending on the temperature conditions.

Fourth Embodiment

Next, a fourth embodiment of the present invention (Case 2 of single stage expansion and the two stage reciprocating compressors 3 a, 3 b with an intercooler 61 which has the configuration similar to the third embodiment) is explained in reference to FIG. 6. In FIG. 6, the branching path 71 branches off from a refrigerant exit pipe path 70 in the downstream side of the heat exchanger 61 and is connected to the discharge chamber 303 of the lower stage compressor 3 a. The rest of the configuration is similar to the third embodiment and thus the same devices and units will not be explained further.

The terminal of the branching path 71 is connected to the injection nozzle 306 provided in the discharge chamber of the lower stage compressor 3 a and the configuration of the discharge chamber 303 is the same as the first, second and third embodiments.

According to the present embodiment, in addition to the cooling effect of the discharge gas in the discharge chamber 303 of the lower stage and upper stage compressors 3 a and 3 b, the refrigerant liquid having been over-cooled (30° C.) by the heat exchanger 61 is supplied to the discharge chamber 303 of the lower stage compressor 32 a via the branching path 71, thereby further improving the cooling effect of the discharge gas of the discharge chamber 303. Therefore, the supply of the refrigerant liquid to the branching path 71 can be reduced, thereby downsizing the injection nozzle 306.

Moreover, in the present embodiment, in the upper stage compressor 3 b, the head cover (discharge chamber 303) may be cooled by water instead of injection of the refrigerant liquid (injection nozzle 306), or maybe cooled by air depending on the temperature conditions as suggested in the above-described embodiments.

Fifth Embodiment

Next, a fifth embodiment of the present invention (Case 3 of using single stage expansion and the two stage reciprocating compressors 3 a, 3 b with an intercooler 61 which forcibly cool inside of the intercooler 81 by injecting the refrigerant liquid by the expansion valve 83) is explained in reference to FIG. 7. The present embodiment replaces the heat exchanger 61 of the fourth embodiment shown in FIG. 4 with the intercooler 81 and the rest of the configuration other than the intercooler 81 and the surrounding components thereof is the same as the fourth embodiment. The intercooler 81 has a branching path 82 branching from the refrigerant circulating path 2 a in the upstream side of the intercooler 81 and the expansion valve 83 is provided in the branching path 82.

The intercooler 81 of the present embodiment has a heat-transfer pipe path 81 a in communication with the refrigerant circulating path therein and a space in which the discharge refrigerant gas of the lower stage compressor 3 a is filled is provided outside of the pipe path 81 a and the heat exchange takes place between the refrigerant liquid moving through the pipe path 81 a and the discharge refrigerant gas through the pipe wall of the pipe path 81 a.

Moreover, the refrigerant liquid been heat-transferred in the pipe path 81 a of the intercooler 81 is introduced to the expansion valve via the exit side pipe path 70.

Furthermore, the branching path 71 branches off from the refrigerant exit pipe path 70 in the downstream side of the heat exchanger 61 and is in communication with the discharge chamber of the lower stage compressor 3 a.

With the configuration above, the refrigerant liquid being introduced to the branching path 82 passes through the expansion valve 83 so as to be decompressed and then introduced to the intercooler 81. The refrigerant liquid evaporates in the intercooler absorbing the evaporative latent heat, thereby improving the cooling effect of the refrigerant liquid introduced to the pipe path 81 a of the intercooler 81 from the refrigerant circulating path 2 a. The refrigerant liquid is cooled in the intercooler 81, for instance to 25° C.

Consequently, with the present embodiment in comparison with the fourth embodiment, the cooling effect of the refrigerant liquid by the intercooler 81 is improved, thereby further reducing the temperature of the refrigerant liquid at the exit side of the intercooler 81. Thus, the temperature of the refrigerant being supplied to the discharge chamber 303 of the lower stage compressor 3 a from the branching path 71 can be further reduced, thereby further improving the temperature regulating effect of the discharge gas of the lower stage compressor 3 a. Furthermore, the cooling effect of the refrigerant liquid being introduced to the expansion valve is improved, further enhancing the cooling capability of the refrigeration unit 1.

Sixth Embodiment

Next, a sixth embodiment of the present invention (Case of using the two stage reciprocating compressors and a two-stage expansion with an intercooler 91. The two-stage expansion is performed such that the refrigerant liquid from the liquid receiver 6 is injected from the expansion valve 92 to an expansion space 91 a inside the intercooler 91 and the refrigerant liquid received in the bottom of the space is introduced to the evaporation unit 8 via the expansion valve 7.) is explained in reference to FIG. 8. The present embodiment replaces the heat exchanger 61 of the third embodiment with the intercooler 91. And the expansion valve 92 is provided in the refrigerant circulating path 2 a in the upstream side of the intercooler 91. The rest of the configuration is the same as the third embodiment.

With this configuration, the refrigerant liquid of the refrigerant circulating path 2 a passes through the expansion valve 92 so as to be decompressed and then introduced to the intercooler 91. The refrigerant liquid evaporates in the intercooler absorbing the evaporative latent heat of the discharge gas of the lower stage compressor 3 a inside the intercooler. The intercooler 91 of the present embodiment is formed like a closed vessel with a hollow space inside and contact heat exchange takes place between the refrigerant liquid and the discharge gas inside the hollow space.

According to the present embodiment in comparison with the third embodiment, by providing the intercooler 91 instead of the heat exchanger 61, the cooling effect of the refrigerant liquid reaching the expansion valve is further enhanced (e.g. cooling to 1° C.) and the cooling effect of the refrigerant gas being supplied to the discharge chamber 305 of the upper stage compressor 3 b is enhanced as well (e.g. cooling to 6° C.).

Furthermore, in comparison with the fifth embodiment shown in FIG. 7, it does not require the heat transfer pipe arranged in the intercooler 91, thereby reducing equipment cost.

Seventh Embodiment

Next, a seventh embodiment of the present invention is explained in reference to FIG. 9. FIG. 9 illustrates an elevation plan of a cylinder top assembly 100 of the reciprocating compressor to be integrated in the refrigeration unit of the present invention. The reciprocating compressor of the present embodiment comprises a pair of cylinders.

As illustrated in FIG. 9, a piston 102 is slidably positioned in the cylinder 101. The cylinder 101 is placed on an exterior body 103. On top of the cylinder exterior body 103, a valve plate 111 is positioned which has openings 111 a. The openings 111 a are concentrically positioned to correspond to the top opening of the cylinders 101. The valve plate 111 has cavities in which the plate-type intake valve 105 forming a ring shape and a volute spring 106 on top of the intake valve are housed.

An elastic force of the volute spring 1066 works on the intake valve 105 so as to press the intake valve 105 against a top of the cylinder 101. An intake chamber 104 and an intake gas passageway 104 a in communication with the intake chamber 104 are arranged under the intake valve 105. When the piston 102 moves downward in the cylinder 101, the pressure in the cylinder 101 becomes small, causing the pressure difference between the cylinder 101 and the intake chamber 104. During the step, the refrigerant gas g₁, lifts the intake valve 105 and is introduced into the cylinder.

A valve cage 112 in a shape of circular plate is provided above the valve plate 111 so as to close the opening 111 a of the valve plate 111. A valve plate 114 in a shape of a conical frustum is joined to the bottom of the valve cage 112 with a bolt 113.

A discharge gas passageway 116 a is formed in the valve cage 112 and a volute spring is equipped on the valve cage 112. Under the volute spring 117, a plate-like discharge valve 118 in a shape of a ring is provided beside the discharge gas passageway 116 a.

When the piston rises and the pressure of the discharge gas of the cylinder 101 becomes large, the discharge gas g₂ pushes up the discharge valve 118 and is discharged to the discharge gas passageway 116 a.

Above the valve cage 112, a head cover 121 is arranged so as to form a discharge chamber 116 on top of the valve cage 112. The discharge chamber 116 is in communication with the discharge gas passageway 116 a and also feeds the high-pressure discharge gas being discharged from the cylinder 101 to the refrigerant circulating path.

The refrigerant gas g2 being discharged from the discharge gas passageway 116 a to the discharge chamber 116 passes through a passageway 107 formed in the cylinder exterior body 103 and is fed to the refrigerant circulating path. The passageway 107 is arranged adjacent to the intake chamber 104 and the intake gas passageway 104 a via a wall of a partition wall of the exterior body 103.

As illustrated in FIG. 9, both of the head cover 121 and the cylinder exterior body 103 have through-bores 121 a and 121 b respectively which are connected to the branching pipe paths 122 a and 122 b respectively which correspond to the branching pipe path 9 of FIG. 1. The through-bore 121 a opens to the inner wall of the head cover and the through-bore 121 b opens to the passageway 107. And the injection nozzles 123 a and 123 b are installed in the openings of the through-bores 121 a and 121 b respectively. By this, the condensed refrigerant liquid from the liquid receiver not shown in the drawing is sprayed to the discharge chamber 116 and the passageway 107 via the branching pipe paths 122 a and 122 b.

On the surface of the head cover 121, a cooling water filling space 125 is hermetically formed such that a cooling water jacket 124 covers the head cover. A cooling water supply hole 124 a is provided in the cooling water jacket 124 so as to fill the space 125 with the cooling water w from the hole 124 a.

In the present embodiment, the refrigerant liquid is sprayed to the discharge chamber 116 and the passageway 107 in a form of fine particles through the injection nozzle 123 a and 123 b so as to improve the absorption effect of the evaporative latent heat of the discharge gas.

The passageway 107 is arranged adjacent to the intake chamber 104 and the intake gas passageway 104 a via a wall of a partition wall of the exterior body 103. But the heating of the discharge gas passing through the intake chamber 104 and the intake gas passageway 104 a is prevented by spraying the refrigerant liquid to the passageway 107 through the injection nozzle 123 b and suppressing the temperature rise of the discharge gas.

Eighth Embodiment

An eighth embodiment of the present invention is explained in reference to FIG. 10. In the present embodiment shown in FIG. 10, in comparison with the first embodiment shown in FIG. 1 to FIG. 3, the branching path 9 branching the refrigerant liquid in the downstream side of the liquid receiver 6 is omitted in the refrigeration unit 1 and the branching pipe path 9 is not connected inside the discharge chamber 303 of the single stage reciprocating compressor 3, and the injection nozzle is not installed. The rest of the configuration is the same as the first embodiment of the present invention.

In the present embodiment, the cooling of the discharge gas in the discharge chamber 36 by using the evaporative latent heat of the condensed refrigerant liquid is not conducted.

And the heat transfer between the intake chamber 36 and discharge chamber 24 is prevented by installing the insulation gasket 39 between the valve plate 31 and the cylinder exterior body 2, thereby suppressing the temperature rise of the intake gas in the intake chamber 24. Moreover as shown in FIG. 3, the insulation space i is formed between the cylinder exterior body and the gasket in an area interposed by the cylinders, thereby enhancing the insulation effect.

By this, the temperature rise of the intake gas before reaching the cylinder is suppressed, thereby avoiding the decline in the volumetric efficiency of the reciprocating compressor and maintaining the refrigerating capability of the refrigeration unit 1.

Ninth Embodiment

Next, a ninth embodiment of the present invention (in the case of using single stage expansion and the two stage reciprocating compressors 3 a, 3 b with an intercooler 81. The intercooler 81 is forcibly cooled inside by injecting the refrigerant liquid by the expansion valve 83 and the refrigerant at room temperature of the liquid receiver 6 is supplied to the discharge chamber 303) is explained in reference to FIG. 12. The present embodiment shares the same configuration with the fifth embodiment besides the intercooler 81 and the surrounding components. The refrigerant circulating path 2 a comprises a pathway 2 a arranged through the intercooler 81 and another pathways 2 b and 71 a branching from the pathway 2 a to bypass the intercooler. The refrigerant at room temperature of the liquid receiver is fed to the nozzle 306 of the discharge chamber of the lower stage compressor 3 a.

With the configuration as described above, preferable effects described below can be obtained in comparison with the case of supplying the low temperature refrigerant having passed through the intercooler 81 to the discharge chamber 303 of the lower stage compressor 3 a.

The intercooler 81 and the heat-transfer pipe path 81 a (for low temperature liquid) are insulated so as to avoid the heating from the external air (or the temperature of the surrounding devices).

Especially, when the heat penetrates from outside through the valve or the like to the pipe or heat exchanger which is full of liquid, it is prone to the heat expansion and thus causing explosion from where it is weak. However, in the present embodiment the pathway 2 a arranged through the intercooler and another pathways 2 b and 71 a branching from the pathway 2 a to bypass the intercooler 81 are provided in such a manner that the refrigerant at room temperature of the liquid receiver 6 is directly led to the discharge chamber 303 of the low stage compressor 3 a, thereby solving the above problem.

INDUSTRIAL APPLICABILITY

According to the present invention, the temperature rise of the intake refrigerant gas inside the reciprocating compressor is suppressed and the refrigerant gas of high density can be introduced, thereby improving the volumetric efficiency and further enhancing the performance of the heat pump unit such as a refrigeration unit having the reciprocating compressor integrated therein. Therefore, the highly efficient heat pump unit and refrigeration unit of the reciprocating unit in which the temperature rise of the intake gas in the compressor is suppressed and at the same time cooling water is not used, can be obtained. 

1. A heat pump unit comprising: a heat pump cycle which includes a reciprocating compressor having a compression part where a piston reciprocates inside a cylinder, a condenser, an expansion valve, and an evaporator provided in a refrigerant circulating path in which NH₃ refrigerant liquid is circulated; and a first returning path for the refrigerant liquid which returns a portion of the NH₃ refrigerant liquid having been condensed in the condenser to a discharge chamber provided in a cylinder top assembly of the reciprocating compressor or a discharge area that is in communication with the discharge chamber, wherein the discharge chamber or the discharge area is provided with an injection nozzle connected to the first returning path for the refrigerant liquid such that the NH₃ refrigerant liquid is discharged through the injection nozzle to the discharge chamber or the discharge area.
 2. The heat pump unit according to claim 1, further comprising a liquid pump and a pressure-regulating valve located in the first returning path for the refrigerant liquid, and the NH₃ refrigerant liquid which has higher pressure than the discharge chamber is discharged through the injection nozzle to the discharge chamber or the discharge area.
 3. The heat pump unit according to claim 1, wherein the reciprocating compressor is a single-stage compressor provided with the injection nozzle in the discharge chamber or the discharge area of the single-stage compressor.
 4. The heat pump unit according to claim 1, wherein the reciprocating compressor is a multi-stage compressor including an upper stage compression part and a lower stage compression part, and the injection nozzle is located in the discharge chamber or the discharge area of the upper stage compression part so as to inject the NH₃ refrigerant liquid through the injection nozzle to the discharge chamber or discharge area of the upper stage compression part.
 5. The heat pump unit according to claim 4, further comprising: a second returning path for the refrigerant liquid which returns the portion of the NH₃ refrigerant liquid having been discharged from the upper stage compressor part and then condensed in the condenser, to the discharge chamber or discharge area that is in communication with the discharge chamber, the discharge chamber or the discharge area being located in the lower stage compression part; wherein the portion of the NH₃ refrigerant liquid is led to be returned to the discharge chamber or discharge area of the lower stage compression part via the second returning path.
 6. The heat pump unit according to claim 5, further comprising a heat exchanger for the refrigerant liquid which is provided in the refrigerant circulating path between the condenser and the expansion valve, the heat exchanger being connected to the refrigerant circulating path so that refrigerant gas discharged from the lower stage compressor is introduced to the intake chamber or intake area of the upper stage compressor through the heat exchanger, the refrigerant liquid from the condenser being cooled with the refrigerant gas discharged from the lower stage compressor.
 7. The heat pump unit according to claim 6, further comprising a heat exchanger for the refrigerant liquid provided in the refrigerant circulating path in an upstream side of the second returning path, wherein a portion of the refrigerant liquid having been cooled in the heat exchanger is supplied to the first or second returning path.
 8. The heat pump unit according to claim 1, wherein the reciprocating compressor is for refrigerant and comprises an intake chamber in communication with a cylinder via an intake valve at a cylinder top assembly and a discharge chamber in communication with the cylinder via a discharge valve, wherein the injection nozzle and a supply port for refrigerant liquid are arranged in the discharge chamber or discharge area, and the injection nozzle is connected to the supply port for the refrigerant liquid, and wherein the refrigerant liquid is injected through the injection nozzle to the discharge chamber or discharge area. 